[time-nuts] Phase Noise of 74AC gates

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Feb 20 04:06:23 UTC 2010

Martyn Smith wrote:
> Hi All,
> I read Garry's email about using the 74AC04 as a distribution amplifier.
> Did I read it right, does Gary say you will get -178 dBc/Hz at 10 kHz 
> offset???
> Being one of only 3 or 4 companies in the world that manufactures 
> distribution amplifiers that break the -170 dBc/Hz region at 10 kHz 
> offset, in my experience any logic gate or Op amp will limit you to 
> about -155 dBc/Hz at offsets of 10 kHz and beyond.
> I've tested many competitive units and very few people get below -155 
> dBc.
> I'm not about to say how we achieve -170 dBc/Hz phase noise, but we 
> definitely don't use op amps or logic gates!!
> Regards
> Martyn
Actually the phase noise was supposedly -178dBc/Hz or lower for offsets 
of 100kHz or more.
This is potentially possible if a high Q (>1000?? for a 10MHz input ) 
tuned circuit suitable bandpass filter were used.

Extrapolating the measured phase noise of a divider to that of an 
inverter doesn't predict the inverter noise accurately as the divider 
output includes noise due to aliasing of its wide band input noise etc.

One actually has to measure it with an accurately calibrated phase noise 
measurement setup.


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